Long chain oligosaccharides (erythroglycan) attached to proteins on human red cells are being investigated to determine their chemical structure. These compounds, newly discovered, carry 1/3 of the carbohydrate and a majority of the A B O antigenic substance on red cells. Human chronic myelogenous leukemia cells #K562 have been found to synthesize erythroglycan, and the pathways of biosynthesis are being explored.